1. Field of the Invention
The invention relates generally to electrolytic diaphragms and more particularly to an electrolyzer with a sandwich arrangement comprising a diaphragm and electrodes, as well as an appropriate method and apparatus for producing the sandwich arrangement. The arrangement provides a dimensionally stable, electrically insulating diaphragm and permeable electrodes.
2. Description of the Prior Art
Electrolyzers are known to consist of one or usually several electrolytic cells assembled and combined into a cell block. An individual cell is formed by boundary plates or bipolar separating plates, which define an electrolysis chamber. This electrolysis chamber is in turn separated by a diaphragm into anode and cathode chambers. The anode and cathode can be in contact with the diaphragm in a sandwich construction, if the diaphragm is not itself an electrical conductor. Generally, however, the electrodes are not in contact with the diaphragm, but rather are at a distance of approximately 1 to 3 mm from the diaphragm in practice.
Of particular current industrial interest in the context of this invention are electrolyzers for alkaline electrolysis, specifically the electrolysis of water, to which specific reference is made in the present description.
For alkaline electrolysis of water, the applicant has developed a sandwich configuration with a porous, electrically non-conducting oxide diaphragm disposed in contact on both sides with active electrodes, which is used here as a specific example to explain the invention.
Prior art sandwich arrangements known heretofore have been constructed with electrodes which are either of sheet metal configured in the form of louvers, or a type of rib mesh or slotted sheet metal. Consequently, in prior arrangements, in the region between the diaphragm and the electrochemically active main portion of the electrode, there has always been a certain spacing on the order of several millimeters, which spacing represents an additional electrical resistance and thereby leads to energy losses in comparison with the so called desirable "zero distance" concept.
However, the "sandwich structure" sometimes also has a functional disadvantage which is absent in the ordinary prior art structures which are energetically more wasteful. The diaphragm can remain functional only if the diaphragm pores are not blocked, and only if no deposits are caused to be formed on the electrodes. The electrode deposits deleteriously propagate into the diaphragm which is located adjacent to the electrode. Naturally, this demands that the entire cell system including the periphery must be corrosion-resistant so that practically no deterioration by corrosion takes place. Corrosion products would, as a result of the electrode reactions, either precipitate or be deposited cathodically as metals or anodically as oxide hydrates, and would migrate from the electrodes into the diaphragm and would be deposited to coat the diaphragm or could even lead to short circuits. In practice, however, it is very difficult, or at least very expensive and commercially uneconomical, to maintain corrosion-free conditions.
In other words, the reduction of electrode distance, which on the one hand is energy-favorable and therefore economical, is linked with operational problems of the diaphragm becoming disfunctional, whereas the prior art solution, which incorporates a certain substantial distance between diaphragm and electrodes, is cheaper and functionally satisfactory, but less advantageous and less economical from an energy standpoint.